Vapor and particle sampling

ABSTRACT

A sampling apparatus collects sample air from a subject such as a person. The apparatus includes a bypass that divides the sample air stream into a bypass portion and a collector portion. The collector portion of the air stream is delivered to a collector, which traps entrained particles. After the sampling cycle concludes, a mechanical conveyor removes the collector from fluid communication with the bypass and transports it to a analyzing unit. A chamber in the unit receives the collector, and a diverter couples the chamber with either of two vapor and/or particle analyzers. During analysis, a heater in the unit heats both the chamber and the diverter. A sample collected from one subject can be analyzed in one of the analyzers while another sample is being collected from another subject. The other analyzer can then be used to analyze the second sample.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was made with Government support under Contract DTFA-03-87-C-00003. The Government has certain rights in this invention.

This application is a continuation-in-part application of U.S. application Ser. No. 08/334,257, filed Nov. 3, 1994, and entitled "Vapor and Particle Sampling."

BACKGROUND OF THE INVENTION

The present invention relates to vapor and particle collection systems.

When substances such as explosives are handled, minute particles of the substance, which typically have diameters on the order of about 10 microns, often become lodged in nearby areas, including the handler's hair, skin, and clothing. And even when wrapped tightly and stored, most substances emit a certain degree of vapor, the extent of the vaporization depending on such factors as the ambient temperature and the vapor pressure of the substance.

Systems for collecting, or sampling, vapor and particles, for example explosives vapors and/or particles from a person or piece of luggage, are typically either of two general types: non-contact and contact. In non-contact collection systems, a stream of air is typically passed over the subject, intermixing with vapor emanating from the subject and dislodging particles trapped on the subject's skin, clothing, hair, etc. The sample air stream carries the entrained vapors and/or particles to a collection region, where the sample air is channelled to a sample collector. The sample collector generally includes a large surface area desorb site, configured and treated to have a high affinity for the substance or substances of interest. Sample collectors are described in U.S. Pat. No. 5,092,217, issued to Achter et al., assigned to the present assignee, and incorporated herein by reference in its entirety. As the sample air flows over the desorb site, at least a portion of the entrained vapor and/or particles collects on the surface. The sample collector is then later processed, for example by heating the site to vaporize, or desorb, the particles and vapors collected thereon. The resulting desorb air may then be analyzed, for example in a high-speed gas chromatograph, to assess whether the subject is carrying or contains the substance of interest.

Contact vapor and particle sampling systems operate on a similar principle, except a vacuum nozzle in the system is typically brought into direct contact with a surface of the subject. When vacuum is applied, sample air is collected from the immediate vicinity of the nozzle, drawing vapor and/or particles into the system for collection.

SUMMARY OF THE INVENTION

One general aspect of the invention is a contact-type vapor and particle sampling apparatus for collecting vapor or particles from a moving subject, in which a wand having a plurality of sampling holes is oriented so that the holes extend in the direction of movement of the subject.

Among other advantages, because the sampling holes extend in the direction of movement of the subject, the subject can be sampled by successive holes or groups of holes while the subject moves through the apparatus. Thus, for instance, if the wand is sufficiently long and provided with a sufficient number of holes, a person walking at a normal pace would just pass through the apparatus in the time necessary to execute a single sampling cycle. As the subject moves along the wand, successive sampling holes are sequentially covered and uncovered, one or more holes always remaining in contact with, or in close proximity to, the subject. In this manner, sampling can be accomplished without disturbing the normal flow of the subjects, be they passengers walking through an airport or baggage or other items travelling along a conveyor belt, making the sampling process less cumbersome and intrusive.

Preferred embodiments include the following features.

In a particularly useful embodiment, a plurality of wands are pivotally attached to a housing. The wands, e.g., curved tubular sections of polyvinyl chloride or aluminum pipe, are angled downward and are biased towards one another. As the subject (e.g., a person) moves between them, the wands separate, but remain in contact with the person's body. A damper damps the rotation of the wands, providing increased resistance as the subject moves more quickly through the apparatus.

Sample air collected through the sample holes, which are disposed at different rotational orientations around the circumferences of the wands, is delivered through a central fluid flow passage to a vapor and particle collector (e.g., a collector configured for use with an explosives vapor analyzer). A valve in a bypass line connected upstream of the collector can be adjusted to divert a portion of the sample air before it reaches the collector. Because of the bypass line, the aggregate flow rate through the wands can exceed the flow rate through the collector. The flow rate through the wands thus is not directly constrained by the maximum flow rate through the collector. The flow rates through the wands therefore can be increased as necessary, for example to reduce the number of particles that collide with the inner surfaces of the wands.

In another aspect of the invention, the external width of a wand in a contact-type vapor and particle sampling apparatus is less than a characteristic dimension of the contour of the surface of the subject being sampled.

Among other advantages, when sampling an irregularly shaped subject, such as a person, the wand, and thus also the sampling holes in the wand, remain in much closer contact with the surface of the subject than would a wider wand, improving sampling effectiveness. Where the invention is to be used to sample people, because of the surface contour characteristics of the average person, generally the width of the wand (e.g., the wand outer diameter if the wand is tubular) is below about 4 in. (10 cm.), and is preferably on the order of about 1 to 2 in. (2.5 to 5 cm.).

In another aspect of the invention, the central fluid flow passage in a wand in a contact-type vapor and particle sampling apparatus is sufficiently wide to prevent substantially all of the particles of on the order of about 10 microns in diameter from colliding with the wand walls.

Should they collide with the inside wall of the wand, particles very frequently stick to the wall surface, and thus may not be carried to the collector. By preventing a substantial percentage of particles from colliding with the wall, this aspect of the invention thus advantageously increases the percentage of particles delivered to the collector. Moreover, the invention reduces the likelihood that a particle will stick to the wall during one sampling cycle, and dislodge during a subsequent sampling cycle, thereby possibly making the first reading erroneously low, and the second erroneously high.

In preferred embodiments of this aspect of the invention, the sampling holes lie at an acute angle to the central passage. Particles thus enter the central passage travelling in a direction that is nearly aligned with the direction of the airflow through the passage, further reducing the likelihood that entering particles will travel across the passage and strike the opposite wall. In addition, an orifice disposed in one end of the central fluid flow passage regulates to a large degree the flow rate through the wand. The higher the flow rate, the less the chance that entering particles will travel across the passage and strike the opposite wall.

In another aspect of the invention, two symmetrically disposed arrays of sampling wands are disposed at an acute angle to the direction of movement of the subject, traversing a surface of the subject as the subject moves through the apparatus.

Among other advantages, the arrays of sampling wands sweep downward across the subject as the subject moves, sampling vapors and particles from entire vertical regions.

Another aspect of the invention is a collector that includes a gas impermeable material having a high binding affinity for explosives vapor exposed on a surface of a filter woven to trap explosives particles. The collector advantageously collects at least a portion of the explosives vapors and particles entrained in the airstream flowing therethrough.

In preferred embodiments of this aspect of the invention, the filter paper is held in a frame, and the gas impermeable material comprises polyimide strips arranged on the surface of the filter paper.

In another aspect of the invention, a bypass has two ports, a bypass port and an outlet port, opening into a chamber. A fluid inlet in communication with a sampling aperture opens into the chamber between the bypass port and the output port. A collector is configured to collect particles entrained in the flow stream exiting the outlet port, and a pump (e.g., a vacuum pump downstream of the collector) flows air through the sampling aperture, the bypass, and the collector.

Among other advantages, the bypass prevents a portion of the incoming flow stream from reaching the collector. The flow rate of the incoming flow stream is typically selected to ensure that a substantial portion of the particles vacuumed off the subject are drawn through the detection system. In some instances, a considerable pressure drop would have to be maintained across the collector in order to maintain this same flow rate through the collector. By drawing off a portion of the incoming flow stream, the bypass decreases the flow rate through--and the pressure drop across--the collector. The pressure forces on the collector are thus reduced, and a smaller vacuum or other flow pump can be used.

In preferred embodiments of this aspect of the invention, the fluid inlet is at the end of a tube projecting into the chamber, and is directed towards the outlet port. The chamber is defined by a frustoconical surface joined at its large-diameter end with a cylindrical section, where the tube defines an annular region with the cylindrical section. The bypass port is defined in the wall of the cylindrical section, and the output port is defined at the small-diameter end of the frustoconical section. Fluid passing into the chamber through the fluid inlet flows towards the outlet port, and the flow direction of the incoming flow is reversed with respect to the flow direction in the annular region between the inlet and the bypass port.

The momentum of some particles entrained in the incoming flow stream, particularly the more massive particles, may be too great to allow them to reverse direction along with the bypass flow stream. They are carried instead into the outlet flow stream, and from there into the collector. The bypass may thus concentrate particles in the outlet flow stream, such that the particle concentration (i.e., particles per unit volume) there is greater than in either the incoming flow stream or the bypass flow stream. So for a given "split" or flow ratio, a greater proportion of particles may leave the bypass in the outlet flow stream than in the bypass flow stream.

In another aspect of the invention, a bypass has two ports, a bypass port and an outlet port, opening into a chamber. A fluid inlet in communication with a sampling aperture opens into the chamber at a location gravitationally above the output port (i.e., a mass has greater gravitational potential energy at the fluid inlet than at the output port). A collector is configured to collect particles entrained in the flow stream exiting the outlet port, and a pump flows air through the sampling aperture, the bypass, and the collector.

Among other advantages, particles entrained in the sample air stream entering the chamber are gravitationally biased towards the output port. In preferred embodiments of this aspect of the invention, the fluid inlet is gravitationally below the bypass port, and so particles must travel against the force of gravity to traverse the path between the fluid inlet and the bypass port.

In another aspect of the invention, a mechanical conveyor can remove a collector from fluid communication with a fluid flow line and a sampling inlet, and transport it to an analyzer.

Among other advantages, the conveyor facilitates removal of the collector from the sampling system and its transport to the analyzer. The conveyor (which can be a rotary platter with receptacles around its periphery for receiving collectors) can also be automated, such as by driving it with a motor, to further aid in moving it to the analyzer.

Another aspect of the invention is an analyzing unit in which a diverter can couple either of two independent vapor and/or particle analyzers with a sample-receiving chamber. During use, a heater heats both the chamber and the diverter.

Among other advantages, after using one analyzer to analyze one sample, the diverter can couple the other analyzer with the chamber to analyze a different sample. During this second analysis, the first analyzer can be readied for reuse, increasing the rate at which samples can be analyzed. Because it is heated, vapors or particles that become trapped on or in the diverter are typically readily vaporized. Heating thus "purges" the diverter to drive off contaminants that might otherwise taint the results of subsequent analyses.

Another aspect of the invention is a method for collecting vapor and/or particles from two or more subjects. A sample is first collected from one subject by drawing sample air through a sampling inlet and a fluid flow line. While this sample is being analyzed, another sample is collected from a different subject by drawing sample air through the same inlet and fluid flow line. The analysis of the first sample thus need not conclude before the second sample is collected, increasing the rate at which subjects can be sampled.

Other features and advantages of the invention will become apparent from the following detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut away front view of an explosives sampling system.

FIG. 2 is a schematic of the explosives sampling system of FIG. 1.

FIG. 3 is a side view of the explosives sampling system of FIG. 1.

FIG. 4a is a top view of the explosives sampling system of FIG. 1.

FIG. 4b is a schematic view of wands of two different sizes passing over an irregular surface.

FIG. 5 is a detail perspective view of the free end of a wand for use with the explosives sampling system of FIG. 1.

FIG. 6 is an end view taken along the line 6--6 in FIG. 5.

FIG. 7 is a sectional view taken along the line 7--7 in FIG. 5.

FIG. 8 is a partially cut away front view of a pivot mechanism for use with the explosives sampling system of FIG. 1.

FIG. 9 is a partially cut away front view of a different vapor and particle collector installed in the explosives sampling system of FIG. 1.

FIG. 10a is a front view of the vapor and particle collector of FIG. 9.

FIG. 10b is a side view, not to scale, of the vapor and particle collector of FIG. 9.

FIG. 11 is a partially cut away side view of a ticket desorb assembly for use with the vapor and particle collector of FIG. 9, showing the ticket desorb assembly in the open position.

FIG. 12 is a partially cut away side view of a ticket desorb assembly for use with the vapor and particle collector of FIG. 9, showing the ticket desorb assembly in the closed position.

FIG. 13 is a partially cut away front view of another explosives sampling system.

FIG. 14 is a top view of another explosives sampling system.

FIG. 15 is a partially sectional top view of a flexible wand connector.

FIG. 16 is a front view of another portal explosives detection system.

FIG. 17 is a schematic view of the portal explosives detection system of FIG. 16.

FIG. 18 is a sectional side view of a bypass for the portal explosives detection system of FIG. 16.

FIG. 19 is a top view of a rotary transport platter for the portal explosives detection system of FIG. 16.

FIG. 20 is a perspective view of aspects of a transport mechanism for the portal explosives detection system of FIG. 16.

FIG. 21 is a sectional side view of an analysis unit for the portal explosives detection system of FIG. 16.

FIG. 22 is a schematic of an analysis unit for the portal explosives detection system of FIG. 16.

FIG. 23 is a flowchart of a method for sampling a plurality of subjects using the portal explosives detection system of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

As shown in FIG. 1, an explosives vapor and particle collection system 10 includes two vertically extending housings 12a, 12b, between which a person 14 to be sampled walks or is moved, e.g., by a endless-belt conveyor (not shown). Housing 12a, and its associated components, are a mirror image of housing 12b and its associated components. For convenience, like components are assigned the same numerical label, with the suffix "a" appended to the numeral corresponding to the component that lies in the left half of system 10, and the suffix "b" appended to the numeral corresponding to the component that lies in the right half of system 10.

With reference also to FIG. 2, each housing 12a, 12b supports an array of three pivotally mounted, finger-like wands 16a, 18a, 20a; 16b, 18b, 20b. Each wand is a thin, curved tube, for example of polyvinyl chloride or aluminum, that includes a plurality of holes 22 oriented to sweep over the outer surface of person 14 as he or she walks through the system. (For convenience, the collective plurality of holes in each wand are indicated by a single reference numeral, 22. When specific holes are discussed, they are given unique reference numerals.)

Each wand connects at one end to a pivot assembly 24a, 26a, 28a; 24b, 26b, 28b. As described in detail below in connection with FIG. 8, pivot assemblies 24a, 26a, 28a; 24b, 26b, 28b allow the wands to pivot with respect to manifold assemblies 30a, 30b supported by housings 12a, 12b, while keeping the hollow interior of each wand in fluid communication with the hollow interior of the associated manifold assembly. Manifold assemblies 30a, 30b, which are parallel to one another and separated by approximately 30 in. (0.75 m.) to allow person 14 to pass therebetween, are each constructed of three segments of pipe 32a, 34a, 36a; 32b, 34b, 36b, also of polyvinyl chloride or aluminum. The pipe segments are supported by support arms 38a, 40a, 42a; 38b, 40b, 42b, which are cantilevered from the sides of housings 12a, 12b.

The uppermost segment 36a, 36b of each manifold assembly 30a, 30b is a T-section of pipe, having a horizontal branch in fluid communication with upper and lower vertical branches. The upper vertical branch of each of uppermost segments 36a, 36b sealably and releasably mates with the inlet of a sample collector 44a, 44b. Sample collectors, which collect at least a portion of the vapor and particles entrained in the airstreams flowing therethrough, are described in U.S. Pat. No. 5,092,217, issued to Achter et al., assigned to the present assignee, and incorporated herein by reference in its entirety. The outlet of each of collectors 44a, 44b sealably and releasably mates with a collector exhaust line 46a, 46b. A vacuum blower 48a, 48b in each collector exhaust line 46a, 46b draws sample air through the collectors 44a, 44b, and a valve 50a, 50b in each collector exhaust line 46a, 46b is adjustable to control the flow rate through the collectors (vacuum blower 48b and valve 50b in collector exhaust line 46b are not shown in FIG. 1).

The horizontal branches of uppermost segments 36a, 36b are sealably coupled to respective bypass lines 52a, 52b. Similar to collector exhaust lines 46a, 46b, a vacuum blower 54a, 54b draws bypass air through each bypass line, and a valve 56a, 56b in the lines may be adjusted to vary the flow rate of bypass air through the lines (vacuum blower 54b and valve 56b in bypass line 52b are not shown in FIG. 1).

The vacuum blowers in collector exhaust lines 46a, 46b and bypass lines 52a, 52b are controlled by a controller unit 57 in housing 12a. When triggered by a sample cycle initiation signal, generated when a detector 58 mounted to housing 12a detects that a light beam emitted by an emitter 60 mounted to housing 12b has been broken, controller unit 57 activates the blowers for a predetermined sampling cycle time.

In operation, when person 14 passes the front edges of housings 12a, 12b from the side shown in FIG. 1, he or she breaks the beam of light generated by emitter 60, initiating the sampling cycle. During the sampling cycle, vacuum blowers 48a, 48b, 54a, 54b draw outside air (i.e., from atmosphere) through holes 22 in the sides of the wands, as well as through orifices 62a, 64a, 66a; 62b, 64b, 66b in the free ends of wands 16a, 18a, 20a; 16b, 18b, 20b. The aggregate flow rate through each three-wand array is typically on the order of 20 liters/second. Valves 50a, 50b, 56a, 56b can be adjusted to select the proportion of the sample air drawn into manifold assemblies 30a, 30b that flows through collectors 44a, 44b. Typically, the valves are adjusted to allow approximately half of the flow to pass through bypass lines 52a, 52b, and half to pass through collectors 44a, 44b. When the sampling cycle concludes, collectors 44a, 44b are removed from system 10 and processed in an explosives vapor and particle analyzer 67 (shown schematically in FIG. 1) to determine the explosives content of the sample air drawn from person 14.

System 10, and in particular wands 16a, 18a, 20a, 20b, are shown in further detail in FIGS. 3 and 4. As illustrated in FIG. 3, the wands are angled downward, lying at an acute, approximately 30°, angle to the direction of movement of person 14, indicated in FIGS. 3 and 4 by arrow 68. Wands 16b, 18b, 20b (not shown in FIG. 3) are similarly oriented. The wand angle is chosen such that the first holes 70, 72 (i.e., the holes closest to housing 12a) in wands 16a, 18a lie in approximately the same horizontal planes 74, 76 as the last holes 78, 80 (i.e., the holes farthest from housing 12a) in wands 18a, 20a, the wands directly above wands 16a, 18a, respectively. (For clarity, although they lie on the side opposite the side shown, the holes in wands 16a, 18a, 20a are not shown in phantom in FIG. 3.) The last hole 82 in wand 16a lies close to the ground, and the first hole 84 in wand 20a lies in or near the same horizontal plane as the shoulder 79 of person 14. Other holes (not shown) lie at regular intervals between the first and last holes in each wand.

When person 14 first enters system 10 (i.e., when person 14 is in position A), holes 70, 72, 84 in wands 16a, 18a, 20a are at his knees 83, waist 81, and shoulders 79, respectively. And when person 14 is near the end of wands 16a, 18a, 20a (i.e., when person 14 is in position B), holes 82, 78, and 80 in wands 16a, 18a, 20a are at his feet 85, knees 83, and waist 81, respectively. Thus, as person 14 moves in the direction indicated by arrow 68, successive holes (not shown) in the wands make contact with progressively lower portions of his body. In essence, as person 14 walks through the system 10, the wands sweep vertically down his sides (or, if he rotates 90°, his front and back), sampling different regions of his clothing, skin, hair, etc.

Several considerations factor into the selection of the lengths of wands 16a, 18a, 20a; 16b, 18b, 20b. As noted above, the sampling cycle lasts for a predetermined time, generally 4 or 5 seconds. Preferably, the wands are long enough that a person walking at a normal pace just passes through system 10 in the time it takes to execute a single sampling cycle. However, as wand length increases, the wands can become difficult to support at only one end. Balancing these considerations, a wand length of around 60 in. (1.5 m.) has been found to be suitable for many applications.

As shown in FIG. 4a, when viewed from the top, wands 20a, 20b are curved and angled toward one another, forming a funnel-shaped region that receives person 14, and guides him through system 10. Wands 16a, 18a, 16b, 18b (not shown in FIG. 4a) are similarly curved and angled. As explained in detail below in connection with FIG. 8, the wands, although pivotable, are biased towards one another (the rest position of the wands is shown in solid lines in FIG. 4a). Thus, although person 14 forces the wands apart as he moves in the direction indicated by arrow 68, the wands (and thus holes 22 in the wands) remain in close contact with the person, following the contour of his body as they sweep downward. For instance, if the person's waist 81 is wider than his shoulders 79, wands 20a, 20b are forced apart less when he first enters system 10 (position A) than when he has nearly exited the system (position B; the position of wands 20a, 20b when person 14 is in position B is shown in phantom in FIG. 4a). The free ends of the wands 20a, 20b are crossed, which tends in some circumstances to improve the contact between the wands and person 14. Alternatively, the free ends of the wands can be uncrossed.

It can thus be seen that it may be desirable to select the outside diameter of wands 16a, 18a, 20a; 16b, 18b, 20b in accordance with the characteristics of the contours of the surfaces of the subject to be sampled. Most surface contours can generally be described as a series of alternating peaks and valleys of varying radii. If the wand radius is larger than the characteristic dimension of the surface contour, i.e., the mean radius of the valleys, or recesses, in the surface contour, then the wands may ride along the top of the peaks as the wands move downward over the surface, preventing the holes in the wands from coming into direct contact with a significant portion of the surface. This is schematically shown in FIG. 4b, which illustrates how a smaller wand 71 remains in closer contact with the small-radius portions of irregular surface 73 than a larger wand 75 (shown in phantom) as the two wands sweep down the surface in the direction indicated by arrow 77. The holes in wands 71, 75 are substantially perpendicular to the direction indicated by arrow 77, and are directed toward surface 73. As illustrated, small wand 71 (and thus also the sampling holes in the wand) follows the contour of surface 73 much more closely than large wand 75, getting into a greater number of tight-radius areas. In the case of people, the peaks and valleys of surface 73 might, for example, represent regions where extremities bend or are attached to the body, as well as wrinkles and other surface irregularities in the sample subject's clothing. If the wands are sufficiently rigid and of relatively small diameter, because clothing and body tissue are generally fairly compliant, small surface irregularities in the subject's body or clothing typically yield to the wands.

In any event, because the effectiveness of a contact vapor and particle sampling system is generally improved by making direct, intimate contact with the surface to be sampled, if the wand diameter is too large, sampling effectiveness may be compromised. Accordingly, when people are to be sampled using system 10, to ensure good contour following, it is generally preferable if the outside diameter of the wands is less than about 4 in. (10 cm.). Wands around about 1 in. (2.5 cm.) have been found to be suitable.

The free end of wand 18a is shown in detail in FIGS. 5, 6, and 7, and is representative of the free ends of wands 16a, 20a, 16b, 18b, 20b. The hollow interior 87 of wand 18a extends along the curved, longitudinal axis 94 of the wand, providing a fluid flow passage for conveying sample air drawn through the holes in the wand to manifold assembly 30a, and eventually to collector 44a. As exemplified by holes 78, 86, 88, 90, 92, the holes 22 (FIGS. 1 and 2) in the wall of wand 18a are spaced at regular intervals along the length of the wand, spanning between the first hole 72 (FIG. 3) and the last hole 78 in the wand. Thus, holes 22 in wands 16a, 18a, 20a; 16b, 18b, 20b extend in the direction of movement of person 14, indicated by arrow 68 (FIGS. 3 and 4). As person 14 walks through system 10, he or she sequentially covers and uncovers successive holes 22, and is thus at any given time sampled by only one or a few holes.

The diameter of the holes are typically selected in accordance with the desired fluid flow properties of the system. Generally speaking, increasing the diameter increases the flow rate through the hole, but decreases the pressure drop across the hole (i.e., the pressure drop between hollow interior 87 and atmosphere). Holes that are about 0.10 in. (2.5 mm.) in diameter have been found to be suitable for many applications.

The hole diameter also determines to some degree the spacing between adjacent holes. The smaller the hole diameter, the greater the total number of holes that can be made in each wand, and thus the more densely spaced the holes can be. For holes that are about 0.10 in. (2.5 mm.) in diameter, hole spacings between 1 and 2 in. (2.5 and 5 cm.) have been found to be suitable for many applications.

To improve the chances that at least some of them will make contact with the person's clothing, skin, etc., the holes are staggered, that is, adjacent holes are located at different rotational orientations around the circumference of wand 18a. For instance, holes 72, 88, 92 are at one rotational orientation, and holes 86, 90 are at another. Of course, all of the holes 22 in the six wands are located in the sides of the wands directed toward person 14. Moreover, because wands 16a, 18a, 20a; 16b, 18b, 20b are round, the exterior surfaces of the wands slope away on either side of holes 22, increasing the likelihood that the holes will make direct, intimate contact with the clothing, skin, etc. of person 14. Wands with similar cross-sections, such as ovoid or elliptical, can also be employed in system 10.

Holes 72, 86, 88, 90, 92 lie at an acute, approximately 45°, angle to axis 94. As noted above, sample air drawn through the holes may include explosives vapors and particles. When it enters hollow interior 87, the sample air is traveling in the direction indicated by arrow 95 in FIG. 7, a direction oblique the direction of the airflow through hollow interior 87, indicated by arrow 97 in FIG. 7. The incoming sample air therefore changes direction after entering hollow interior 87.

Because it is in a gaseous state, explosives vapor tends to change direction more readily than explosives particles, which typically have greater momentum. Thus, depending on its mass and velocity, there is a chance that an entering particle of explosives may not change direction quickly quickly enough, and may travel across hollow interior 87 and strike the opposite inside wall of the wand. Should this occur, and should the particle stick to the inner wall, not only would the particle not be collected by the collector, possibly resulting in an erroneously low reading, but it could vaporize or dislodge during a subsequent sampling cycle, possibly resulting in an erroneously high reading. And should a sufficient number of particles become stuck to the inner surfaces of the wands, the wands may become so contaminated that have to be discarded. By angling holes 72, 86, 88, 90, 92, particles enter hollow interior 87 travelling in a direction 95 that is much more aligned with the direction of the main airflow 97, decreasing the chance that they will travel across the hollow interior and strike the opposite wall.

Other factors also influence the statistical probability that incoming particles will strike the opposite interior wall of the wands. One is the interior diameter of the wands. Increasing the inner diameter decreases the surface-area-to-volume ratio of the wand interiors, reducing the likelihood that incoming particles will strike the interior wall of the wands. To some degree, the wand inner diameter may be constrained by the desire to keep the outer diameter small to have good contour-following characteristics, as discussed above. Also, when the inner diameter of the wand is increased, the total volumetric flow rate of sample air through the system is often also increased to maintain a certain flow velocity. Generally, the inner diameter will be increased as large as possible, consistent with the desire to reduce the outer diameter of the wand, the desire to reduce volumetric flow rate, and the desire to maintain a certain flow velocity. It is generally preferable to have a wand inner diameter greater than about 0.4 in. (1.0 cm.). Where the outside diameter of the wand is about 1 in. (2.5 cm.), a wand inner diameter of around 0.8 in. (2.0 cm.) has been found to be suitable for many applications.

The probability that incoming particles will strike the inner wall of the wands is also reduced by increasing the flow rate of the air traveling in the direction indicated by arrow 97 through the hollow interior of the wand. For a given vacuum blower throughput, the flow rate through the wands can be tailored to some degree by varying the size of the orifices 62a, 64a, 66a; 62b, 64b, 66b in the respective free ends of the wands. Generally speaking, increasing the orifice diameter increases the flow rate through the orifice, thus also increasing the cross-current flow rate through the wands. This tends to reduce the number of particles that collide with the interior surfaces of the wands. However, increasing orifice diameter also decreases the pressure drop across holes 22 (i.e., the pressure drop between hollow interior 87 and atmosphere), diminishing the vigor with which the holes vacuum the subject's skin, clothing, etc. Balancing these considerations, where the inside diameter of the wand is around 0.8 in. (2.0 cm.), and the holes are on the order of 0.10 in. (2.5 mm.) in diameter, an orifice diameter of around 0.6 in. (1.5 cm.) has been found to be suitable for many applications.

Pivot assembly 26a, which connects wand 18a to housing 12a, is shown in detail in FIG. 8. Pivot assemblies 24a, 28a, 24b, 26b, 28b are of similar construction to pivot assembly 26a. Pivot assembly 26a includes a sleeve 96 having an internal, spool-shaped cavity 98 that extends the length of the sleeve. The large-diameter regions of cavity 98 are slightly larger in diameter than the outer diameters of pipe segments 32a, 34a. With the pipe segments 32a, 34a inserted into the ends of cavity 98, sleeve 96 can be rotated with respect to the segments. 0-rings 99, 101 on the ends of the pipe segments 32a, 34a maintain a substantially airtight seal between pivot assembly 26a and manifold assembly 30a. A flange 103 on the end of wand 18a bolts against the outside of sleeve 96, so that the internal passage of wand 18a is in fluid communication with a passage 100 in sleeve 96 that extends to cavity 98. Wand 18a can thus be easily unbolted and replaced should it become worn, contaminated with explosives particles, or otherwise unusable.

In order to prevent sleeve 96, and thus also wand 18a, from rotating too quickly, a rotary damper 102 is attached between sleeve 96 and support arm 38a. The rotor portion 104 of the damper is attached to the sleeve, and the stator portion 106 to arm 38a. A viscous fluid, such as an oil, fills the gap between rotor 104 and stator 106, and a seal 108 between rotor 104 and arm 38a prevents the fluid from escaping. The damping coefficient of rotary damper 102 is selected so that person 14 encounters substantial resistance if he attempts to pass through system 10 too quickly, but little resistance if he proceeds at a pace that allows the wands to contact his body throughout the sampling cycle.

As noted above, wands in the same horizontal plane are biased towards one another. This is accomplished gravitationally, by a cable 110 that extends over a pulley 112 between a weight 114 and an arm 116 attached to sleeve 96 (see also FIG. 4a). Rotating wand 18a and sleeve 96 from the rest position causes weight 114 to rise, urging the wand and sleeve back to the rest position. The weight-cable-pulley assembly could be replaced with a spring, either a linear spring between arm 116 and housing 12, or a torsional spring between sleeve 96 and arm 38a. In addition to or instead of rotary damper 102, a linear damper or dashpot 117 (shown schematically in FIG. 8), such as a gas spring, can be installed between arm 116 and housing 12.

Other embodiments are within the claims.

For instance, instead of using a separate sample collector for each side of the system, a single collector arranged to receive at least a portion of the flow from both manifold assemblies could be used.

Moreover, the collector may be of any of a number of types, in addition to those disclosed in U.S. Pat. No. 5,092,217. For instance, as shown in FIG. 9, in some applications it may be preferable to substitute a filter paper ticket 130a, 130b, held fixed in system 10 by a pair of clamps 131a, 131b, for collectors 44a, 44b. As shown in FIGS. 10a and 10b, filter paper ticket 130a (filter paper ticket 130b is identical to filter paper ticket 130a) includes a piece of filter paper 132 laminated between two sheets 133, 134 of quasi-rectangular card stock. (Filter paper ticket 130a is not shown to scale in FIG. 10b.) The filter paper, the card stock, and the adhesive used to laminate them together should not, when heated, emit vapors that have gas chromatography signatures similar to the explosive substances of interest. A low-lint, cellulose-based filter paper, such as Crystal No. 8, available from H. L. Bouton Colo., 320 Main Street, Buzzards Bay, Mass., has been found to be suitable. A teflon cloth membrane can instead be used. One such membrane is a 0.010 in. (0.025 cm) 75 micron filtering material available as product M-EC8520 from Fluorotechniques of Troy, N.Y. The card stock can be 0.010 in. (0.025 cm) TAG, or manilla paper, and the adhesive can be an air-dry, pressure-sensitive silicone adhesive, available from Minnesota Mining and Manufacturing, Co.

When filter paper ticket 130a is laminated together, filter paper 132 completely covers an approximately 1.5 in. (3.5 cm.) diameter hole 136 in each piece of card stock 133, 134. Three parallel strips of self-adhesive polyimide tape 138a, 138b, 138c, such as Scotchbrand No. 5413 tape, available from Minnesota Mining and Manufacturing, Co., are applied to one of the filter paper surfaces. Generally, filter paper tickets 130a, 130b are installed in system 10 (between clamps 131a, 131b) so that polyimide strips 138a, 138b, 138c are facing the direction of airflow (i.e., the exposed, non-adhesive surface of strips 138a, 138b, 138c face into the flow.

Polymide has been found to exhibit a high affinity for explosives vapors. The polyimide strips are substantially gas impermeable, in that although explosives vapors can diffuse into or adhere onto the polyimide, there is essentially no mass flow through the strips. Several considerations factor into the selection of the number, width, and spacing of the polyimide strips. The greater the percentage of the filter paper surface area covered by the polyimide strips, the larger the region to which explosives vapors can bind, but the smaller the total flow area of the ticket (and thus, the greater the pressure drop across the ticket). Furthermore, the wider the polyimide strips, the larger the "dead space," or boundary layer, near the centers of the strips, as the airflow separates to go around the strips and through the filter paper. This boundary layer may prevent explosives vapors from coming sufficiently close to the strips to bind to them. Balancing these considerations, it has been found suitable to use three 0.125 in. (0.30 cm.) wide strips 138a, 138b, 138c, separated by 0.125 in. (0.30 cm), to cover approximately 25% of the filter paper surface.

In operation, filter paper tickets 130a, 130b are used in system 10 in essentially the same manner as collectors 40a, 40b. As vacuum blowers 48a, 48b draw sample air through the tickets, at least a portion of the explosives vapors intermixed with the sample air binds with polyimide strips 138a, 138b, 138c, and at least a portion of the explosives particles entrained in the sample air stream become trapped in the fibers of filter paper 132. When the sample cycle has concluded, tickets 130a, 130b are removed from the system 10 and inserted into a ticket desorb assembly 142.

As shown in FIGS. 11, and 12, in particular ticket 130a is inserted into a slot 146 in a sheet metal guide 148 fixed to the walls of a filter paper guide 150 in the interior of the desorb assembly 142. Ticket 130a is shown only partially inserted into assembly 142 in FIG. 11. When fully inserted, ticket 130a triggers a microswitch 152 at the bottom of guide 148, activating a motor (not shown). A cam and cam follower assembly (not shown) driven by the motor force filter paper guide 150 and a back plate assembly 154 toward a snout assembly 156. As shown in FIG. 11, when assembly 142 is in the open position, back plate assembly 154 is approximately twice as far from snout assembly 156 as filter paper guide 150. Accordingly, the cam and cam follower assembly are configured to move filter paper guide 150 at about half the speed as back plate assembly 154.

Back plate assembly 154 includes a machined aluminum block 158 slidably mounted within a frame 160, with two columns of three springs 162 (only one column shown) located between the back side of block 158 and frame 160. A sintered, stainless steel disk 164 is pressed into a mating recess in the front surface of block 158. An electrical resistance heater (not shown) surrounds disk 164.

Snout assembly 156 includes a snout 166 supported by a snout frame 168. An electrical resistance heater (not shown) surrounds snout 166. A desorb gas delivery line 170 extends from the front end of the snout, supplying desorb air from desorb assembly 142 to, for example, a high-speed gas chromatograph (not shown).

In operation, disk 164 and snout 166 are preheated before ticket 130a is inserted into desorb assembly 142. Ticket 130a is inserted into the desorb assembly with polyimide strips 138a, 138b, 138c (FIG. 10a) facing sintered disk 164. When block 158 and ticket 130a are driven into contact with snout assembly 156 by the motor, cam, and cam follower assembly, as shown in FIG. 12, springs 162 compress slightly to provide a desired contact force between block 158 and snout frame 168. Block 158 can also pivot slightly within frame 160, allowing it to align parallel to snout frame 168. 0-rings 172, 174 in block 158 and snout frame 168 provide a substantially airtight seal between back plate assembly 154, ticket 130aand snout assembly 156.

With desorb assembly 142 closed, dry air is supplied through a supply line 176 and a passage 178 in block 158 to a plenum chamber 180 behind disk 164. The air is heated as it passes through the heated sintered disk. The combination of the heated air and the heat radiated by the heated disk and the heated snout vaporizes substantially all explosives vapors and particles trapped in filter paper ticket 130a. The vapor-laden desorb air passes through snout 166 and delivery line 170 into the high-speed gas chromatograph for analysis. Because filter paper ticket 130a is inserted into desorb assembly 142 with polyimide strips 138a, 138b, 138c facing disk 164, the desorb air flows through filter paper ticket 130a in the same direction as did the sample air when the ticket was installed in system 10. Thus, dirt or other foreign matter that does not vaporize at low temperature will remain trapped in the filter paper fibers, and will not be carried into the gas chromatograph.

As shown in FIG. 13, panels 118a, 120a, 122a; 118b, 120b, 122b may be attached to the portions of wands 16a, 18a, 20a, 16b, 18b, 20b that lie closest to housings 12a , 12b. Studies have shown that panels thus located may cause some people to rotate 90° as they walk through system 10. The wands then sample the person's front and back, which are generally of larger surface area than his sides.

Moreover, the wands, which need not be tubes but can be of any cross section, can be bent into a number of different shapes other than those shown and described above. For instance, when viewed from the top, the wands may be S-shaped, as shown in FIG. 14 (only wands 20a20b shown). Generally, the shape of the wand will be selected in accordance with the body shape of the typical subject. Thus, if the typical subject has a fairly round waist, the bows in the S-shaped wands would tend to encircle the subject's waist as the wands sweep down to that region, placing a greater number of holes in contact with the subject. In addition, brushes or puffers (i.e., jets that deliver shorts bursts of air) can be located near all or some of holes 22 in wands 16a, 18a, 20a; 16b, 18b, 20b to help dislodge particles from the subject's hair, skin, clothing, etc. It may also be beneficial to include a small contact valve in the opening each of holes 22. As the subject contacts them, the valves open, providing a fluid flow passage to the interior of the wands.

And although in the embodiments shown and described above pivot mechanisms attach the wands to the housings, if the wands themselves are sufficiently flexible, they can be attached directly to the manifold assemblies. As a person walks through the system, the wands flex as necessary, following the contours of his body.

Alternatively, as shown in FIG. 15, the wands 190 can be relatively rigid, and relatively flexible couplings 192 can be used to couple the wands to a manifold pipe 194. A pivot assembly 196 clamps to both the end of wand 190 and manifold pipe 194, allowing the wand to pivot with respect to the pipe. A spring 198 biases pivot assembly 196, causing the wand to return to the rest orientation after the passenger (not shown in FIG. 15) passes through the system.

Another portal explosives detection system 210 is shown in FIGS. 16 and 17. System 210 includes five wands 212a, 212b arranged on either side of an archway 214. Each wand is at a 25° angle to horizontal. Sample air is drawn through thirty-six 1.5 mm holes spaced apart at 2 cm intervals along each wand. A 4 mm orifice at the end of each wand provides cross-current air flow through the wands.

Sample air from the five wands collects first in a manifold 218a, 218b on either side of archway 214. A Y-fitting 220 connects the two manifolds, providing a smooth transition from the manifolds to a single supply line 222. The other end of supply line 222 terminates in an impact bypass 224. Sample air enters impact bypass 224 through an input port 227. Air exits impact bypass 224 through either a bypass port 229 or an output port 234. Air flowing through output port 234 passes through a collector 236, and from there into a collector line 248. Air exiting through bypass port 229 passes into a bypass line 230.

Impact bypass 224 separates the incoming sample air stream 238 into two portions, a collector portion 240 that flows through output port 234 and a bypass portion 242 that flows through bypass port 229. The flow rate ratio of the collector portion 240 to the bypass portion 242 is determined by the relative settings of a valve 244 in the bypass line 230 and a valve 246 in the collector line 248. Valves 244, 246 are typically set to maintain a desired flow rate through and pressure drop across the collector 236.

The collector line 248 also includes a pressure sensor 249. If intact and functioning properly, the pressure drop across collector 236 is within a certain range. Should the collector rupture, the pressure drop will decrease. The sensor 249 will detect an increased pressure downstream in the collector line, and will send a signal indicating a potential failure of collector 236. If the collector were to become clogged, the pressure drop across it would increase. The sensor 249 will detect a decreased pressure downstream in the collector line, and will send a signal indicating a potential failure of collector 236.

The bypass portion 242 of the sample air is typically vented to atmosphere without first being subjected to analysis. Any particles or vapors entrained in the bypass portion 242 are thus usually discarded, representing a loss of information.

To reduce this loss of information, impact bypass 224 is configured to divert proportionally more particles to collector portion 240 than to bypass portion 242. This is achieved by passing the bypass portion 242 of the sample air through a tortuous flow path that particles having too great a momentum cannot negotiate.

As shown in detail in FIG. 18, impact bypass 224 includes a frustoconical (or funnel-shaped) portion 250 joined at its wide end to a closed-ended cylindrical portion 252. The narrow end of frustoconical portion 250 has a diameter of 1.40"(3.56 cm), and the wide end of frustoconical portion 250 has a diameter of 1.69"(4.29 cm). The inside diameter of cylindrical portion 252 is also 1.69"(4.29 cm). Frustoconical portion 250 is 0.68"(1.73 cm) tall.

The collector 236 is sealingly connected to the narrow end of the frustoconical portion 250, and bypass line 230 is sealingly connected to a flange fitting 253 projecting at a right angle to the side of the cylindrical portion 252. Supply line 222 mates to another flange fitting 255 at the top of the impact bypass 224. A tube 257 sealingly connected to flange fitting 255 extends toward frustoconical portion 250, defining an annular region 259 with cylindrical portion 252. The opening at the free end of tube 257 is directed towards output port 234, in that fluid entering the bypass through this opening flows toward output port 234. Tube 257 has an outside diameter of 1.25"(3.18 cm) and an inside diameter of 1.00"(2.54 cm). The free end of the tube is 1.00"(2.54 cm) above the narrow end of frustoconical portion 250, and 2.50"(6.35 cm) below the bottom edge of bypass port 229. Tube 257, frustoconical portion 250, and cylindrical portion 252 are all coaxial.

In use, the sample air stream 238 with entrained particles and vapors enters impact bypass 224 through input port 227. The collector portion 240 of the sample air stream continues in a straight line towards output port 234 and collector 236. Because the free end of the tube 257 is below the bottom edge of bypass port 229, the flow direction of the bypass portion 242 in annular region 259 is reversed with respect to the flow direction of the sample air stream 238 coming into the bypass 224.

As noted, the incoming sample air stream 238 contains particles intermixed with air. As the sample air stream begins to split, some of these particles are carried by the bypass portion, and the rest by the collector portion. However, the momentum of many of the particles entrained in the bypass portion, particularly the more massive particles, is too great for them to make the turn. Instead of being swept along with bypass portion 242 as it reverses flow direction, these particles intermix with the collector portion 240, and are carried into the frustoconical portion 250, through the output port 234, and onto the collector 236. In addition, because output port 234 is below the free end of tube 257, gravity biases the entrained particles towards the output port. Stated otherwise, the opening at the free end of tube 257 is "gravitationally above" output port 234, and "gravitationally below" bypass port 229. Impact bypass 224 thus acts to concentrate particles in the collector portion 240 of the sample air: The concentration of particles (i.e., the number of particles per unit volume) in the collector portion 240 is greater than in the sample air stream 238, which is in turn greater than in the bypass portion 242.

After a sampling cycle concludes, the collector 236 is automatically transported from the bypass 224 to an analyzer unit 256. As shown in FIG. 19, the collector 236 is received within one of the receptacles 274 arranged around the periphery of a rotary platter 270. In use, a collector similar in construction to collector 236 is inserted into each of the sixteen receptacles 274.

Rotary platter 270 is driven by a stepper motor/belt drive system 272, shown in FIG. 20. To show the spatial relationship between drive system 272, impact bypass 224, and analyzer unit 256, platter 270 is not shown in FIG. 20.

After a sampling cycle concludes, drive system 272 rotates platter 270 one rotary step of 20°, moving collector 236 from impact bypass 224 to analyzer unit 256, and positioning a fresh collector at the base of the bypass. As shown in FIGS. 21 and 22, analyzer unit 256 includes a source of purified air 258, a heater block 260, a desorb air delivery tube 262, a diverter valve 263, and two separate analysis trains 264, 266. (The source of purified air 258, the diverter valve 263, and the two separate analysis trains 264, 266 are not shown in FIG. 22.) The analysis trains can each include an explosives analyzer such as a high-speed gas chromatograph/chemiluminescence detector or an ion mobility spectrometer.

In use, purified air supplied to the heater block 260 passes through a series of four sintered disks 268 (FIG. 21), heating the air to about 150°-180° C. The heated air vaporizes and drives off, or "desorbs," any absorbed vapors and/or particles on collector 236. The heated desorb air then flows through the desorb air delivery tube 262 (also heated), and into the diverter valve 263.

Diverter valve 263 couples the desorb air delivery tube 262 with one of the analysis trains 264, 266. As shown in FIG. 22, diverter valve 263 is positioned to couple tube 262 with analysis train 264. If diverter valve 263 were rotated 90° clockwise, tube 262 would be coupled with analysis train 266. Although diverter valves tend to have a number of passageways, surfaces, crevices, etc. that can trap vapor or particles in the desorb sample, the elevated temperatures within the analyzer unit 256 typically quickly vaporize such trapped materials. Thus it is usually advantageous to locate the diverter valve 263 in a heated region such as inside the analysis unit 256. Alternatively, supply pipe 222 (FIG. 17) could be provided with a "Y" fitting, where the input to the Y comes from the wands and each of the Y outputs goes to a separate impact bypass, collector, transport mechanism, and analysis unit. Flow could be switched from one collector subsystem to the other by opening and closing the valves 244, 246 in the collector and bypass lines.

Heater block 260 of analyzer unit 256 is coupled to impact bypass 224. Before rotating platter 270, a clamping mechanism 276 (FIG. 20) raises heater block 260 and bypass 224, disengaging both from platter 270. Clamping mechanism 276 may be pneumatically or electro-mechanically operated, such as by a solenoid. After the platter has been rotated one step, clamping mechanism 276 reengages heater block 260 and bypass 224 with platter 270. Seals (not shown) provide a fluid-tight interconnection between and among the various subcomponents.

System 210 also includes a purging heater/blower 278, shown in FIG. 20. Heater/blower 278 is arranged to force heated air through collectors after they have exited analysis unit 256, driving off any residual vapors and/or particles. Heater/blower 278 is located on the order of nine rotary steps (180°) away from bypass 224, giving the collectors ample time to cool after purging.

Referring to FIG. 16, portal explosives detection system 210 further includes a video camera 280 positioned over the top of archway 214, and a height detector 282 positioned along the sides of the archway. As a subject to be sampled, such as a person, approaches the archway, a video image is recorded by the camera. When the subject enters the archway, the height detector 282 determines the subject's height. (The height detector 282 may be an array of light beam emitters and detectors arranged at different heights, or may instead be a pattern-recognition algorithm that determines the subject's height by analyzing the image from video camera 280.) Because subjects may object to having wands come into contact with their heads, depending on the output of the height sensors, the system may activate one or more mechanisms 284a, 284b, 286a, 286b, 288a, 288b (which may be pneumatic or electric rotary actuators) to rotate a sufficient number of wands 212a, 212b out of the way to guard against such contact. For instance, if the subject is tall (as shown in FIG. 15), no wands are rotated out of the way. However, one, two, or even three wands may be moved out of the way for shorter subjects.

A flowchart detailing the operation of the portal explosives detection system 210 is shown in FIG. 23. As a first subject (passenger A) enters the archway 214, an image is recorded by video camera 280, his or her height is sensed, and an appropriate number of wands are moved out of the way. Passenger A is then sampled as he or she walks through the system. At the conclusion of the sampling cycle, the transport mechanism moves passenger A's collector to the analyzer unit.

While the analyzer unit is analyzing passenger A's collector, a second subject (passenger B), can pass through system 210. After the conclusion of this next sampling cycle, passenger B's collector is moved to the analyzer unit. (Eventually, passenger A's collector rotates to the purging heater.) The diverter valve in the analyzing unit is switched to the other analysis train, and while passenger B's collector is being analyzed, the first analysis train cools down and is then ready for another use. The results of the analysis of passenger A's collector are then displayed on a computer monitor 290, along with a video image of passenger A. If the analysis shows the presence of materials of interest, passenger A may then be detained for further consideration. If all is in order, passenger A is allowed to proceed.

If during the analysis the sensor 249 indicates that the collector in the bypass may be defective (e.g., that the collector is ruptured or clogged), a signal to this effect is provided to the operator. In subsequent sampling cycles, the transport mechanism is operated to skip the defective collector until it is replaced or repaired.

The vapor and particle sampling systems described herein can be used to sample other subjects, such as luggage or food products. If so, the dimensions, orientations, positions, and number of wands, holes, and orifices may be tailored to best match the surface contour and other characteristics of the subject. The system can also be used for other than explosives sampling applications. For instance, the system may be configured to collect particles and vapors from narcotics or perfumes, or, in the food processing industry, from animal or vegetable matter, such as chicken, beef, or fish, for example to detect decay or contamination. 

What is claimed is:
 1. Apparatus for collecting particles comprising:a sampling aperture; a fluid flow line having first and second ends and a passage extending therebetween, the first end of the fluid flow line being connected to the sampling aperture; a bypass including:a housing defining a chamber having a substantially cylindrical portion and a substantially frustoconical portion having a large end and an opposed small end, wherein a diameter of the cylindrical portion is substantially equal to a diameter of the large end of the frustoconical portion, the large end of the frustoconical portion being joined to an end of the cylindrical portion; a bypass port defined by the housing and opening into the chamber; an output port defined by the housing and opening into the chamber; a fluid inlet in communication with the second end of the fluid flow line, the fluid inlet opening into the chamber between the bypass port and the output port; a collector in fluid communication with the outlet port of the bypass and configured to collect particles entrained in a flow stream exiting the outlet port; a pump in fluid communication with the collector, the pump being operable to flow air through the sampling aperture, the fluid flow line, the bypass, and the collector.
 2. The apparatus of claim 1 wherein the fluid inlet is directed towards the outlet port.
 3. The apparatus of claim 1 wherein the bypass is configured such that fluid passing through the fluid inlet into the chamber flows towards the outlet port.
 4. The apparatus of claim 1 wherein the bypass is configured such that a flow direction of fluid flowing between the fluid inlet and the bypass port is reversed with respect to a flow direction of fluid flowing through the fluid inlet into the chamber.
 5. The apparatus of claim 1 wherein the bypass further includes a tube having a first end in fluid communication with the second end of the fluid flow line and a second end defining the fluid inlet.
 6. The apparatus of claim 5 wherein the tube projects into the chamber.
 7. The apparatus of claim 5 wherein the chamber comprises a region between the tube and the housing.
 8. The apparatus of claim 7 wherein the chamber comprises an annular region between the tube and the housing.
 9. The apparatus of claim 5 wherein the fluid inlet defined by the second end of the tube is directed towards the outlet port.
 10. The apparatus of claim 1 wherein the frustoconical surface is coaxial with the fluid inlet.
 11. The apparatus of claim 10 wherein the frustoconical surface is coaxial with the outlet port.
 12. The apparatus of claim 1 wherein the bypass port is defined in the cylindrical section.
 13. The apparatus of claim 1 wherein the pump is a vacuum pump.
 14. The apparatus of claim 13 wherein the vacuum pump is connected downstream of the collector.
 15. Apparatus for collecting particles comprising:a sampling aperture; a fluid flow line having first and second ends and a passage extending therebetween, the first end of the fluid slow line being connected to the sampling aperture; a bypass including:a housing defining a chamber having a substantially cylindrical portion and a substantially frustoconical portion having a large end and an opposed small end, wherein a diameter of the cylindrical portion is substantially equal to a diameter of the large end of the frustoconical portion, the large end of the furstoconical portion being joined to an end of the cylindrical portion; a bypass port defined by the housing and opening into the chamber; an output port defined by the housing and opening into the chamber; a fluid inlet in communication with the second end of the fluid flow line, the fluid inlet opening into the chamber at a location gravitationally above the output port; a collector in fluid communication with the outlet port of the bypass and configured to collect particles entrained in a flow stream exiting the outlet port; a pump in fluid communication with the collector, the pump being operable to flow air through the sampling aperture, the fluid flow line, the bypass, and the collector.
 16. The apparatus of claim 15 wherein the fluid inlet is gravitationally below the bypass port.
 17. The apparatus of claim 15 wherein the fluid inlet is directed towards the outlet port.
 18. The apparatus of claim 15 wherein the bypass is configured such that fluid passing through the fluid inlet into the chamber flows towards the outlet port.
 19. The apparatus of claim 15 wherein the bypass is configured such that a flow direction of fluid flowing between the fluid inlet and the bypass port is reversed with respect to a flow direction of fluid flowing through the fluid inlet into the chamber.
 20. The apparatus of claim 15 wherein the bypass further includes a tube having a first end in fluid communication with the second end of the fluid flow line and a second end defining the fluid inlet.
 21. The apparatus of claim 20 wherein the tube projects into the chamber.
 22. The apparatus of claim 20 wherein the chamber comprises a region between the tube and the housing.
 23. The apparatus of claim 22 wherein the chamber comprises an annular region between the tube and the housing.
 24. The apparatus of claim 23 wherein the bypass port opens into the annular region. 